The United States has issued satellite images and cited intelligence to back its claim that Iran was behind attacks on Saudi oil facilities.
Iran denies involvement in Saturday's air attacks, which were claimed by Iranian-backed Houthi rebels in Yemen.
But unnamed US officials speaking to US and international media say the direction and extent of the attacks cast doubt on Houthi involvement.
The incident has cut global oil supplies by 5% and prices have soared.
What is the US saying?
Secretary of State Mike Pompeo blamed Iran at the weekend, prompting Tehran to accuse the US of deceit.
Tweeting on Sunday, President Donald Trump stopped short of directly accusing Iran, but suggested possible military action once the perpetrator is known.
Unnamed US officials have been speaking to the New York Times (NYT), ABC and Reuters.
One official said there were 19 points of impact on the targets and the attacks had come from the west and north-west - not Yemen, which lies to the south of Saudi Arabia.
Officials quoted by the New York Times spoke of a mix of drones and cruise missiles that might have been deployed, though not all hit their targets - the Abqaiq processing plant and the Khurais oilfield.
What are the oil markets doing?
The oil price has surged.
Brent crude jumped 10% to $66.28 a barrel, in what Bloomberg describes as the biggest intraday surge since 1988.
West Texas Intermediate rose 8.9% to $59.75 in Asian trading.
Prices eased slightly after President Trump authorised the release of US reserves.
How has Iran reacted?
Iran has yet to respond to the latest US assertions.
But Iranian Foreign Minister Javad Zarif tweeted on Sunday to deride Mr Pompeo, saying that "having failed at max pressure, Sec Pompeo's turning to max deceit".
He was referring to the Trump administration's stated "maximum pressure campaign" which has targeted Iran with sanctions since Washington pulled out of an international agreement to limit the scope of Iran's nuclear programme.